The operative portion of a reciprocating compressor or pump includes at least one piston and cylinder assembly with intake and exhaust valves typically located at or near one of the cylinder heads. It is commonly known to use the same form of valve for both inlet and outlet by simply reversing the position of the valve for the two uses. One such valve is disclosed in U.S. Pat. No. 5,511,583 by Bassett which has singular annular valve elements. FIG. 7 shows typical prior art.
Ever since the self actuating automatic compressor valve was introduced the basic concept has remained unchanged. There have been major changes primarily to internal component configuration and materials however the valve elements still reciprocate in a to and fro manner in response to internal pressure changes.
Compressor valves are the most common and expensive components associated with unplanned compressor shutdowns. The usual problems are broken sealing elements and springs and to a lesser degree damaged seats and guards.
Unloading for start-up is generally accomplished by by-passing the inlet to outlet pressure, Finger/fork type unloaders hold the valve plates open through brute force or plug type unloaders.
Adding Finger/fork type unloaders compounds the potential problems due to the need to maintain proper mechanical clearances and the vulnerability of delicate valve components. Whenever changes are made to valves such as lift or seats remachined the unloader to valve clearance requires remachining.
It is also known to (A) fully unload a compressor cylinder ends by holding the inlet valve plates open during the compression event and (B) partially unload by reverse flow capacity control by holding the inlet valve plates open during a portion of the compression event. Either of these unloading methods may cause short compressor run times.
Unloading by method (A) requires very exacting manufacturing techniques as well as knowledge current operating conditions. Unloading by method (B) requires all the conditions of (A) plus analysis of unloader back-flow drag forces on the valve plates which can be significant and increase with mol weight and inlet pressure.
The present invention can overcome these shortcomings as will be described in the Summary.